1. Field of the Invention
The present invention relates to an X-ray analytical apparatus for making the material evaluation, construction analysis and so forth of semiconductor materials or the like, and more specifically to an X-ray analytical apparatus of a wavelength dispersion type for the spectro-chemical analysis of characteristic X-rays generated from a sample using a high energy ion beam as a probe.
2. Description of the Related Art
As one of procedures for the construction analysis of materials at a atom level, an X-ray analytical apparatus using a curved analyzing crystal as schematically shown in FIG. 5 has been known. An analytical point of a sample 33, a analyzing crystal 34 and an X-ray detector (correctly, a detector slit) are arranged on a Rowland circle, and a characteristic X-ray generated when an electron beam, an ion beam or the like as a probe is irradiated on the analytical point of the sample 33 is subjected to spectro-process and condensation by the analyzing crystal 34 and detected by the X-ray detector 35.
In the above-described construction, the relative position between the sample and the analyzing crystal 34 and the direction thereof are varied with the spectral wavelength. As shown in FIG. 6, the position of the sample 33 is fixed and the analyzing crystal 34 is moved on a straight line passing the analytical point of the sample 33, and the position and direction of the X-ray detector 35 are simultaneously moved so that the sample 33, the analyzing crystal 34 and the X-ray detector 35 are always on the Rowland circle for measurement.
In order to allow the analyzing crystal 34 to make spectro-process without aberration, it is necessary to curve analyzing element into a cylindrical shape with a diameter of the Rowland circle being a radius. FIG. 7 shows an example of a conventional construction to bend the analyzing element. A pair of threaded constructions each comprising a motor 41 and a worm gear 37 causes supports 39 and 40 of a analyzing element 38 to advance and retreat from opposite sides to thereby change the curvature of the analyzing crystal 38.
Furthermore, as the X-ray detector 35, a proportional counter is ofter used, which is effective to detect a low energy X-ray. The proportional counter makes use of gas multiplication of gases filled in the counter, in which electrons of paired ions produced by the ionization function of the X-ray are accelerated under high voltage to produce an electron avalanche within the counter, thereby amplifying the number of the electrons to measure its charge as an electric pulse.
However, in the X-ray analytical apparatus comprised of the above-described conventional construction, it is necessary for scanning the wavelength to move the relative position between the sample, the analyzing crystal and the X-ray detector and the direction thereof while keeping them on the Rowland circle. This results in a uselessly larger size of the apparatus construction and makes it necessary to provide a drive mechanism capable of making a fine adjustment to keep a locating precision, and as a result, there gives rise to a problem in that the apparatus construction becomes complicated.
The construction to bend the analyzing element has a further problem in that a deviation in the moving direction tends to occur due to the precision in position of the supports and the precision in assembly of the drive mechanism, which leads to the difficulty of setting the curve radius with high precision; and that a displacement in the threaded portion caused by the motor leads to the change in curvature of the analyzing element, resulting in a difficulty of fine adjustment of the curve radius.
Furthermore, it is necessary to provide a slit in the X-ray detector in order to remove the scattered X-ray. In this case, there occurs a problem in that if a width of the slit is made narrower in order to improve the effect of the slit, a sensitivity of detection lowers so that the measuring time becomes uselessly long to lower the detection efficiency.
Moreover, in the case where the proportional counter is used as the X-ray detector, it is necessary to increase the gas multiplication rate for detecting the low energy X-ray. In such a case, higher voltage is applied to an anode wire. However, when the applied voltage is increased, the counter tends to deteriorate, thus spoiling the precision of measurement. Therefore, the voltage applied to the anode wire can be raised merely to an allowable limit, thus posing a problem in that a sufficient sensitivity for the detection of the low energy X-ray cannot be obtained.
It is therefore an object of the present invention to provide an X-ray analytical apparatus of a wavelength dispersion type using a microprobe of ion beam and applying an improvement in construction of essential parts for overcoming the problems as noted above with respect to prior art.
Furthermore, the conventional X-ray analysis by way of irradiation of ion beams has a problem in that since a measurement making use of a parallel beam is employed, an irradiation spot is wide such as a millimeter order, and as a result, a resolving power of wavelength degrades, failing to make the measurement with high accuracy. This poses a problem in that when the irradiation spot is controlled to be small by the slit, the sensitivity of the detection lowers and the measuring time becomes prolonged.